hey guys i have the borla exhaust paired up with Berk HFC. I love it so far but i've been hearing this LOUD RUMBLE like i would expect drone to sound like, but only in HEAVY rain! It goes with the RPMs also. I was driving it was sounding fine and i hit like a mile stretch of heavy rain and it was just really rumbling badd, and when i passed the rain, the same minute the noise went back to normal....

I have no idea what this could be, but I know it can't be normal. Any help?!?! Thanks!

 

Is it a mechanical vibration or actual drone?

 

Only thing I can figure is it's louder in the rain because maybe you have a small leak/gap at a flange joint and when the exhaust gets wet it cools the metal and the metal shrinks creating a tiny gap.

When the metal is hot again (hot metal expands) it is more expanded and closes the gap.

 

I'm actually wondering if the wet pipes cool the exhaust gas so much that it lowers the gas speed of sound so much that is changes the system resonance frequency to the point that its "way out of tune" and hence finds a new drone frequency.

IDK ...just an element for the fishbone diagram.

 

Also from what I hear cold pipes (usually cats/TP's) tend to rasp more than when they're hot. Maybe the whole exhaust drones more too when cold.

 

not to hijack, but i have read people using dynamat and similar products for their systems lower the drone noise inside the cabin from exhaust? perhaps this could help.... I have considered an exhaust swap because i get an annoying drone around 2k rpm with my borla and HFC....

 

Hrmm...I have a similar setup and haven't noticed this. Then again, I tend to not drive the Z in the rain.