Hello,We have a 2006 Holiday Rambler with 7500 miles on it. It has the Chevy 8.1 with the Allision Transmission. We just set out on our maiden voyage from Vermont to Maine. 8 hrs no problems, I am pulling into my spot at our site and I hear this knocking coming from somewhere under the coach. At first I'm thinking a blown engine but it isn't coming from there, I pulled the engine cover off and it sounded fine. It seems to be coming from behind one of the mufflers at maybe another part of the exhaust? It knocks faster as you rev. Any ideas? I'm a little nervous not knowing where it is coming from. I felt all along the exhaust pipe and around all the connections they seem fine?

My guess is a typical warped or cracked exhaust manifold. You usually don't hear the noise unless it is under load. It can sound like a knocking sound.

Check your exhaust system again. I had an 07 HR 8.1 and the exhaust pipe had flexible connections just behind the engine and before the muffler. More like a ball/slip type joint. The tailpipe would move easy enough in this joint it allowed the end of the tailpipe to tap/bang against the coach body in sync with the engine RPM's. The tapping/banging made the joint rattle in sync with the others. This joint is designed to slip, even though it seemed odd to me.From the factory the exhaust tips had about 1/2" clearance from the coach body where they exit. They rattled/banged every time I started it. You could see it by standing next to them when the engine started.I had the tips of the tail pipe cut off and new ones installed angled lower with around 1-1/2" clearance... problem gone!

Thanks I'll check the exhaust again, when I did check with the engine running it seemed to be coming from a small muffler type behind the main muffler, maybe the catalytic converter. That was where the sound was the loudest. I did check near the manifold and everything seemed fine there. It's hard to pinpoint where exactly it's coming from. Could the sound be echoing from elsewhere? Could there be something inside the catalytic converter making noise?

Check the heat shields around the convertor. Usually the shields are spot welded. Crack a weld and it will make a racket.

That sound is typical of a cat guts that has come apart.

Funny noise coming from ? | Good Sam Community

17 Replies

bsinmich
Explorer
Jul 27, 2014
The catalytic convertor is usually the first thing in the exhaust to get the most heat. It could be a simple thing of a loose baffle in a muffler. Not letting an exhaust system get hot creates gas and moisture in the system and then rust. That is why starting a car to just move it on a cold engine is hard on the exhaust.
mant
Explorer
Jul 27, 2014
Update! It's a miracle! Started my coach, the noise was still there, started my 400 miles home and the sound disappeared. I guess whatever was loose or broke fixed itself!! Big load off my mind, now if I can find my mysterious water leak???
D_E_Bishop
Explorer
Jul 23, 2014
Poor QA.
mant
Explorer
Jul 23, 2014
Good idea, what makes them go bad, I've driven many, many vehicles and never had a problem with the Cat. I only have 7500 miles on it?
Bird_chaser
Explorer
Jul 23, 2014
If you have access to the underneath, you can take a rubber mallet and tap the cat you should hear no noise if all is good. You'll hear rattling if it's bad.
mant
Explorer
Jul 23, 2014
I looked at the Workhorse site, no recall. I'm 99% sure it's the Cat. I'll drive it home and try to locate the part. It looks pretty straight forward, the cat with a pipe front and back attached with two flanges. Where do I find parts for a workhorse? I would think any auto parts store doesn't stock this type of thing. It's a lot easier crawling under this than my car!
dan-nickie
Explorer
Jul 22, 2014
mant wrote:
Looks like the Cat, can I drive it the way it is for about 400 miles?

IF it is in fact the Cat, it will not hurt to drive it.
rgatijnet1
Explorer III
Jul 22, 2014
There was a recall on the catalytic converters on the Workhorse 8.1 engines. You may want to check by entering your VIN on the Workhorse website and see if that recall was taken care of on your coach. Register here on the WH site. WH website
mant
Explorer
Jul 22, 2014
Looks like the Cat, can I drive it the way it is for about 400 miles?
dan-nickie
Explorer
Jul 22, 2014
royl wrote:
Bird chaser wrote:
That sound is typical of a cat guts that has come apart.
X2

X3

I had a Cat Converter do that years ago on a Corvette.
I listened to it for days and could not pinpoint it.
Sounded just like a piston rod knocking.

Then I got the opportunity to go down in a lube bay under the car.
It was easy to ID it under there.
Replaced cat and all was well.

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Funny noise coming from ?

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