Ansa Catback Drone

[Sea Aych]

Hey folks - my old muffler (an "Ernst") started to go, and I managed to grab locally an Ansa (BW4847) catback for nearly no money so figured I'd install it. My car's got a completely stock M20 and cat.

Thing is, there's an insane low drone / reverberation / resonance, even at idle to the point where it resonates through my entire garage and is shockingly bad. From idle, all the way up to 2500 RPM it's loud and drone-y, and worse under heavier load until it quiets down and sounds more normal above that.

Lots of other people online have written than the Ansa catbacks are nearly stock sounding so I'm wondering if I have a dud unit or if this is normal.. Anyone have this muffler and noticed the same?

[roguetoaster]

Maybe unpopular opinions, but a stock M20 doesn't even need a muffler, and one of my very favorite M20 sounds was a stocker with a rotted muffler case with just the perforated tubes remaining.

As to why your system is droning, I'd look at it hitting something somewhere. Beyond that, disconnect the forward coupler and see if it changes, and if it does, it must be clogged or somehow odd in the resonance chamber.

[82eye]

cat could be shot and rattling if it's original. they'll make a drone once they go. the drone is better than the rattle.

[Sea Aych]

cat could be shot and rattling if it's original. they'll make a drone once they go. the drone is better than the rattle.

Took a peek inside from the back when the muffler was out and from what I could see looked totally intact. no rattle when i shake or tap it with a mallet, or bogging symptoms either. Could be though..

Maybe unpopular opinions, but a stock M20 doesn't even need a muffler, and one of my very favorite M20 sounds was a stocker with a rotted muffler case with just the perforated tubes remaining.

As to why your system is droning, I'd look at it hitting something somewhere. Beyond that, disconnect the forward coupler and see if it changes, and if it does, it must be clogged or somehow odd in the resonance chamber.

It would be fun, but just a little too loud for me anyway. As far as the muffler hitting something, it's certainly possible though it seems shockingly drone-y for that. I'll take another peek but I think I might be in the clear...


To add, it's more of a resonance / reverberation outside the car than a drone inside the car. You can hear it clearly as part of the exhaust note if you're by the tips, and especially if you're under the car back of the cat.

[reelizmpro]

Very strange to hear this. I had a 325i Ansa exhaust back in the day and it was very quiet. I'd say it was "sporty."

[moatilliatta]

Is it touching the chassis somewhere?

[Sea Aych]

Was fiddling around with the idle last night and noticed the deep reverberation/resonance goes away somewhat if I bump it up from 600 to about 850rpm. A reasonable improvement for now but it still seems a bit strange.

It might not mean anything, but it sounds like the droning is starting behind the cat, ahead of the muffler (if i touch my hand against the pipe / listen).

[moatilliatta]

Engine & Trans mounts new?

[Panici]

Was fiddling around with the idle last night and noticed the deep reverberation/resonance goes away somewhat if I bump it up from 600 to about 850rpm. A reasonable improvement for now but it still seems a bit strange.

It might not mean anything, but it sounds like the droning is starting behind the cat, ahead of the muffler (if i touch my hand against the pipe / listen).

Get under there and feel for exhaust leaks while it's running. Could be a hole on the top side of the pipe?

[Sea Aych]

Get under there and feel for exhaust leaks while it's running. Could be a hole on the top side of the pipe?

Yeah, I gave that a shot, and nothing as far as I can tell - had a piece of parchment paper up there too just in case I couldn't feel it with my hand...

And moatilliatta, mounts new in the last couple of years yep.

In any case, the bumped idle helped a bit but I'll keep digging... Maybe swap in another muffler to compare.