sound cuts out intermittently

I have had my system installed in my 2004 BMW 325ci for about 4 or 5 months now. I have two JL amps, installed upside down on the rear deck of the trunk, a single Infinity Kappa perfect 12" sub, and JL components in the doors. the head unit is an Alpine 9855. The system has been working fine, until about three weeks ago when an annoying problem started popping up. Every so often, when listening to any source (CD, radio or Ipod), the sound will stop for about five seconds, and then return again. This is intermitent, but has been occurring more and more frequently. It also seems like everytime I hit a bump in the road, the sound will cut out. I can still hear a tiny bit of sound, but most of it is just gone, and then it returns about five seconds later at the same volume where it left off.

Yesterday, this happened while listening to the radio, and the sound stayed silent for a good 20-30 seconds before returning. It is very annoying, to say the least. what possible causes could there be for this? I'm almost thinking the amps are cutting out or going into protection or something, but I'm not running the system hard at all. This happens even at low volumes, and after the system has been running a short time.

Any help in troubleshooting this problem would be appreciated, as this is starting to make listening to the system unenjoyable. Thanks.

that was what I was afraid of....it doesn't happen only when hitting bumps in the road, but it does do that quite a bit. I'm wondering if there isn't more to it than that. I hate to remove the amps from the deck, since it is a clean install and it was a PIA getting them mounted up there. But I guess I can do it and see if the situation improves.

I can take some pics and try to post them, but basically I have two JL amps: One 300/1 that is powering the components, and one 250/1 that is powering the sub. The amps have all the cooling circuitry and cooling fins on the outside edge, so I was told they are among the few amps that can mounted upside down ok. I have also seen other professional instalations, where this was done. When you open the trunk, the amps are basically mounted to a piece of mdf that is screwed into the metal shelf that makes up the top of the trunk. The fins are outside, so all you see is the cooling fins running along the opening to the trunk.

Does JL Audio say you can mount these amps upside down or just some other installer?  Take a look at page 3 of your owner's manual where mounting upside down is called "fair" and then only under certain conditions.  I cannot recommend you use your amps upside down and I have never seen a problem-free installation doing this.

What is the impedance load on the amps?  How is the gain set? What is the system voltage at the amp terminals when they shut down?

Sorry, the amp is a 300/4. That was a typo.

Dyohn,

to answer your questions, I haven't checked the voltage on the terminals so I am not sure. The impedance on my whole system is 4 ohms. The components are 4 ohms, and the sub is a single voice coil 4 ohm kappa perfect. The amps use inteligent circuitry to adjust the amps for any ohm load between  2 ohms and 8 ohms, for optimal power output. I don't think my setup is causing any issues as far as impedance.

I am also a member of a BMW online forum, and that is where I have seen many, many examples of amps being installed on the upper deck of the trunk. JL Amps in particular, and most if not of these installations were performed by professional shops with good reputations that work with high end equipment on high end vehicles. That is why I decided to do my setup this way. The shop I was considering hiring to do my install also was going to hang them, and they are a reputable shop. I took that as meaning the amps could take it. I am not an expert, I could be wrong.

Although the heat issue may be what's causing this, I'm not convinced that is it. This morning the sound was cutting out after just starting the car and having the system running for a few minutes. No way the amps had time to overheat. I also still wonder why it seems to happen more often when I hit a bump in the road. Almost simultaneously in most cases (although not everytime). Any ideas on that?

I guess tomorow I will just unmount the amps and set them up temporarily on the floor of the trunk to see if that makes a difference, and check al my connections in the process.

Ok, here a few pics of the current setup. Forgive the wires, I was messing with them today.