Loud "pop" from front of MZ4; all of a sudden it sounds like a V8

So I'm driving my Z4MC this evening, and during the process of going around a corner I hear a loud "pop" from under the footwell (or that general area). From that point forward the thing sounds like a race car fitted with a V8 & straight pipes. It's now head-turning loud even at low speeds, and there's a ridiculous amount of in-cabin drone at low RPMs, which disappears quickly when revved. It sounds fantastic, but it's clearly ill. No warning lights have lit up, the engine isn't running hotter than usual/leaking fluids, and the noise doesn't seem to have impacted performance - other than it sounds a helluva lot faster. I'd categorize the volume as comparable to an M3 fitted with a race-like after-market exhaust, though I'm not 100% sure the noise is coming from the rear cans. I'll get it looked at tomorrow (BMW Roadside Assistance just told me to drive it home).

Any ideas what the problem might be?

Oh, one more thing. About 500 miles ago the dealer replaced the VANOS. The current problem doesn't sound anything like the "noisy" VANOS they replaced, but could it be related?

Opinions from the tech gurus amongst you would be appreciated.

Something happened to your exhaust. Possibly the header cracked due to strain. There are things that are meant to prevent this, but one could have failed.

From your description, I'm 150% positive it's an exhaust issue.

Thanks Ben, appreciate the insight.

Ironically I've got a set of Eisenmann Race cans on order, so I'm toying with the idea of driving around with the "cracked header" until the arrve - as it sounds so good. Would that be a bad idea? I.e. can a cracked header create further damage?

Thanks againb.,

With a cracked header I would be more worried about people in the car than the car. Exhaust gas is not a good thing to breath and if you have exhaust gas coming out of your header, you are most likely breathing it in. This is how people die. Don't drive your car until you get it fixed!

Turns out it's rtelatively serious - 1-2 engine mount screws broke/fell out, so the engine was sitting slightly lop-sided in the car and resting on the chasis. This also caused the exhaust to rub on the chassis. How the heck these screws crack/simply fall out is beyond me. The dealer's got the car - they want to ensure no further damage was caused, and of course need to replace the screws. Not good.

Because our cars are made in the USA??

Sucks man. I hope it still runs well when you get back. That's some crazy ****.

Originally Posted by nhs156

Turns out it's rtelatively serious - 1-2 engine mount screws broke/fell out, so the engine was sitting slightly lop-sided in the car and resting on the chasis. This also caused the exhaust to rub on the chassis. How the heck these screws crack/simply fall out is beyond me. The dealer's got the car - they want to ensure no further damage was caused, and of course need to replace the screws. Not good.

Second one I've heard of with this problem.

Ron, that's both interesting and concerning. Was the second one "fixed" easily - i.e. screws replaced/engine reattached with no further issues? Or should I expect knock-on problems.

I'm not particularly happy. Aside from the numerous rattles/squeeks, I've had a faulty VANOS replaced and know this - all within 6K miles!

Originally Posted by nhs156

Turns out it's rtelatively serious - 1-2 engine mount screws broke/fell out, so the engine was sitting slightly lop-sided in the car and resting on the chasis. This also caused the exhaust to rub on the chassis. How the heck these screws crack/simply fall out is beyond me. The dealer's got the car - they want to ensure no further damage was caused, and of course need to replace the screws. Not good.

Do you know if they fell out or broke?

Do you know which two of the four fell or broke out?

Left side uses four M8-26 bolts.
Right side uses two of the same and two M8-35 bolts.

Just checked my right side bolts and they look fine.
Back two are relatively easy to get to. Front ones not so easy.

I lurk all the time in the M-Z3/4 forums and I have come to the conclusion both generations of cars are very temperamental, yet very rewarding cars to drive. Sorta like a Maserati, when they aren't broken down, they are pure bliss to drive.

If you recently had a faulty VANOS replaced, is there a chance that they had to re & re the engine mount bolts for some reason and forgot to torque them back down afterwards?

That would be an embarrassing oversight, but if it's a procedure that they don't do every day (or have ever done, possibly) it could happen.

It looked like one the bolts was located somewhere towards the front right (passenger) side of the car. It looked to me like it was missing (i.e. had come loose and fallen out) though the mechanic wasn't so sure.

I'm not sure/clear as to whether this has anything to do with replacing the VANOS, though I though that was located on the top of the engine, i.e. they wouldn't have had to take the engine off its mounts to replace the VANOS. However, if I'm wrong in this regard, pls advise! I'd be curious as to whether this is BMW's or the dealer's fault, not that this knowledge would necessarily change much...

And yes, the car's fun to drive (as was my '99 MC). The Z3-based MC was more reliable though... and just a little bit more fun to drive.

So what was the final resolution to this? New bolts and you are good to go or more serious?

Can we do any preventative work? Maybe get better quality bolts and replace them?

Weird, second one I have heard of with this problem as well.

Thankfully I've got 8K on my coupe and not a single problem! Just to throw some good in with the bad