Dash Speaker Problem - Loose wires?

[damelioj17]

1999 Boxster
CDR-220 with 4 speaker (dash and door) - original equipment
Added: PNP rear speaker kit + 6-channel 996 amp (using Harvey's extension from head unit to amp)

All:

About a month ago I installed the PNP rear speaker kit along with switching out the stock 4 channel amp with a 6 channel amp from a 996. Long story short, everything was working great with no issues for about 3 weeks.

About a week ago, I noticed that the front dash speakers were cutting out intermittently. For example, all 6 speakers would be working fine, then I would hit a bump and the dash speakers would cut out. Hit another bump and they would come back on.

In addition, this problem only happens with the TOP DOWN. I have confirmed this through several tests as the car is my daily driver. Any time I drive with the top up, no issues.

Finally, this only happens to the dash speakers. The door speakers and rear speakers are fine.

At first I assumed it was a loose connection at the amp and/or HU, but I'm at a loss with this problem only occuring with the top down.

Any ideas or areas I should check for loose wires? I haven't attempted any fixes yet.

Thanks!

JD