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Old 10-25-2017, 11:49 PM   #1
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Default Harmonic or Sympathetic Vibration

We have a 2012 Winnebago ERA 170X. On a 2011 MB 3500 Sprinter Chassis,milages was 4000 when we got it and now its 10,000. Have been bugged by this since day one.
At 2200 RPM we get a horrid loud rattling sound. Have looked under van and checked exhaust routing for clearance and heat shields--all are ok. I placed pink fiberglass insulation between shields and van floor ad sound absorbers. I added pipe insulation on the black and gray water valve pull rods and insulated the parking brake cables.
Still screams at me around 2200 rpm as i up shift through gers!!

I'm at wits end. going to try extending exhaust pipe straight out the back --I think

Any Ideas??
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Old 10-26-2017, 12:41 AM   #2
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We have a 2012 Winnebago ERA 170X. On a 2011 MB 3500 Sprinter Chassis,milages was 4000 when we got it and now its 10,000. Have been bugged by this since day one.
At 2200 RPM we get a horrid loud rattling sound. Have looked under van and checked exhaust routing for clearance and heat shields--all are ok. I placed pink fiberglass insulation between shields and van floor ad sound absorbers. I added pipe insulation on the black and gray water valve pull rods and insulated the parking brake cables.
Still screams at me around 2200 rpm as i up shift through gers!!

I'm at wits end. going to try extending exhaust pipe straight out the back --I think

Any Ideas??
You may want to try looking at the intake side, as turbo engines can get the same kind of pulsing droning as exhaust can, with any loose pieces getting rattled.
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Old 10-27-2017, 05:44 AM   #3
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Default Using smartphone to pinpoint noises.

Dear JPMcG: To locate where some unpleasant resonance is coming from, you could always use the example pictured below.

But seriously folks.. Have you tried strapping your cell phone in various locations? With some trial & error you should be able to pin down the offending part. Even better: 2 cell phones recording your run up through the gears. Which ever one is louder is closer. Once you locate the spot, turn on video recording and see if something is vibrating.

Cell phones are new and I am old. - I seldom think of their versatility.
DougB
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Old 10-27-2017, 12:23 PM   #4
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There are also those bore-scope things.

Bud
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Old 10-27-2017, 03:55 PM   #5
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Originally Posted by dougbaty View Post
Dear JPMcG: To locate where some unpleasant resonance is coming from, you could always use the example pictured below.

But seriously folks.. Have you tried strapping your cell phone in various locations? With some trial & error you should be able to pin down the offending part. Even better: 2 cell phones recording your run up through the gears. Which ever one is louder is closer. Once you locate the spot, turn on video recording and see if something is vibrating.

Cell phones are new and I am old. - I seldom think of their versatility.
DougB
Like the idea but the noise I'm sure is under the van--I'm not willing to tape ny iPhone under there. I'm also old and half l deaf can't tell the subtle differences in the onions volume.
A real good, but expansive, way would be multi microphones and a O-Scope but that gets way beyond my initial concerns. I'll fiddle with exhaust tuning a bit more.
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Old 10-27-2017, 06:20 PM   #6
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..................
A real good, but expansive, way would be multi microphones and a O-Scope but that gets way beyond my initial concerns. I'll fiddle with exhaust tuning a bit more.
You could consider this device Wireless ChassisEAR, it is about $200 but you can get a receiver with just 1 clip sensor for less. The sound sensor is mounted inside the clip, so you can pinpoint sound source as accurately as with an automotive mechanical stethoscope. This tool is on my list of toys as I am heading to noise elimination line on my "final" to do list.
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Old 10-29-2017, 02:17 AM   #7
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You could consider this device Wireless ChassisEAR, it is about $200 but you can get a receiver with just 1 clip sensor for less. The sound sensor is mounted inside the clip, so you can pinpoint sound source as accurately as with an automotive mechanical stethoscope. This tool is on my list of toys as I am heading to noise elimination line on my "final" to do list.
I FOUND IT!!!!!
I have suspected a sympathetic harmonic frequency vibration. Although I was not completely convinced it wasn't a resonant exhaust power burst (like a straight pipe Holly) But today I found a double plate baffle on the water tank beside the final catalytic converter.
The exhaust has always been a little close to the tank bracket but 1/4" was not touching. Today when I found that gap between the tank framing and an extra heat shielding plate--I stuffed the gap 1/2 inch wide and 12" high x 48" with good old pink fiberglass insulation.
IT WORKED no more screaming vibration at 2200 - 2300 RPM in any gear under any load. Now I can start on the rattles-from cabinets and 'stuff that needs better storage.
Thanks for all the advice.
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