HK subwoofer box - hack to fix the buzz from it

Psifire

Newbie
Joined
Aug 1, 2025
Points
3
Hi,

I've been looking around to see if anyone else tried the same solution to fix the buzz coming from the behind the head HK subwoofer box in the Z3. I don't see this anywhere; so, sorry if this has been mentioned before.

Anyway, the issue with the HK subwoofer box is that the plastic box is attached to a metal frame via 4 metal screws. This plastic-on-metal configuration is just poor engineering as it looks like no one at BMW ever tested the radio at high volume.

So, the solution I used? Weather stripping

Unscrew the box. Put weather stripping around and across each screw hole. Reattach the sub with the screws, but _do not_ torque it all the way down. What you're making is a grommet so that your subwoofer "floats" above the metal brackets.

Does this effect the sound? Probably. The alternatives are to live with the buzzing sound, to get someone to build a new subwoofer, or to get a commercial sub that will take up trunk space. My vote is for the weather stripping. :cool:

Thoughts?

Psifire
 
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ZedHead78

Newbie
Joined
Oct 21, 2025
Points
3
I'm trying to find a replacement for the roadster's subwoofer. It's a hot piece of garbage and I'm pretty sure my speaker is blown back there.

The variable I'm weighing is if I should get a new speaker or spend time building a new box. What did you do?

I'm going to a Z meet up this weekend where one of the Z3 guys has a www.Z3subwoofer.com stealth box kit, but waiting to hear it in person first before pulling the trigger. Have you seen that?
 

Psifire

Newbie
Joined
Aug 1, 2025
Points
3
I bought a Kicker low profile 6" subwoofer on Amazon (https://a.co/d/7jzhfHy).

I followed an article I saw in the online Bimmerfest forums (https://www.bimmerfest.com/threads/2001-bmw-z3-3-0i-harman-kardon-subwoofer-repair-worked.468530/).

I used an angle grinder to shave the sub where the speaker's metal frame was impacting the stock subwoofer box. Cost me under $100 and an afternoon of using the grinder. Afterwards, I screwed it onto the box, used silicon caulk to seal between the box and sub; then, plugged it in.

Works great. Looks a bit messy, but it all hides inside the compartment.
 
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