Engine compartment noise for 2006 Fleetwood Jamboree 23.5

[Cusick4]

I have a noise coming from engine compartment of my 2006 jamboree 23.5 .
It is only under acceleration and doesn't do it all the time. Seems to happen when hot or I get behind a big rig. Anybody heard of this?

[Cusick4]

The only way I can describe the noise is like when you were a kid and you put cards in the spokes of your bicycle to make that loud noises.

[F4Gary]

May be an exhaust leak.

[Cusick4]

If it was an exhaust leak wouldn't it do it all the time. I can be driving on the freeway with no noise, all of sudden it starts flapping and makes the noise. Then I get in clear air and it's gone. This may sound weird but I thought when the air pressure around the coach changes sometimes the noise appears.

[Skip426]

The noise your describing ; and particularly the timing of the noise, leads me to say thermostatic fan engagement.
Is this a new to you RV, or has the noise just started up on a coach you've had for a while?

The thermo hub in the center of the rad fan allows the fan to turn slower than engine speed; to save power; , until the air passing through the radiator, onto the hub, reaches a certain temperature. Then the fan locks up to engine speed and goes to full song ( ROAR).
When you travel behind a rig , the air flow to the front of your RV decreases and the temp goes up and the fan locks up to keep the engine temps down.
You could check that the fan blades are clean and that there isn't anything contacting the fan or stuck to the front of the radiator.
But without driving your coach I'd say it's pretty normal.