Thump sound from subwoofer while HU is off

[ilovehaus]

I had a sub + amp installed the other day at a shop. The setup is an Alpine MRP-M500 amp and a 12" Type R subwoofer. Today I noticed when the key is in the on position but when the head unit is off, and when I tap on the panel trim on the inside of the car (driver's side) the sub makes a thump noise. The harder I hit it the louder the thump sound is. Does this mean they routed the power and speaker wires under the same panel, which I heard you're not supposed to do? Or could it be something else? The car is a 2009 VW if it matters. Thanks in advance.

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[ilovehaus]

Bump?

 

[x1le 10+ year member]

Not completely certain what would cause this. Running rca's next to power wire would not cause it to thump. Sounds to me like they used a bad grounding location.

 

[Deeper_shades 10+ year member]

I had the same problem, as soon as I bought a new amp, it stopped...which is strange because the amp I replaced the one that thumped was the alpine mrp 1000.....

 

[cebbeler7 10+ year member]

Either ground loop, bad ground, or bad amp. The fact that you can hit your panel and that causes the subwoofer to receive a signal is... Not good. Whoever installed that should probably be fired haha. Then again it could be a faulty amp.

 

[domllama 10+ year member]

Not completely certain what would cause this. Running rca's next to power wire would not cause it to thump. Sounds to me like they used a bad grounding location.

Had this happen with an old Memphis amp setup..relocated ground and made shorter which stopped it. Also, be sure the place where it is grounded is metal to metal contact. I know it sounds silly but a lot of people miss that.

 

[cebbeler7 10+ year member]

good point