distorting amplifiers

hi,

this is my first post on this forum.

does any one know what could cause the amplifier (class d)  sound to become distorted after 6-8 months use.

i am using 0awg/4awg all round, big battery. the subs are wired correctly as well.

all the class d amps i use they work fine for a while and then the sound becomes distorted.

What is the model # of the amp? Model # of sub(s), and how they're wired to the amp. What vehicle? Where is the amp grounded? Where is it mounted (what to)?

And mostly, has the gain knob on the amp (and/or bass-boost) been turned up since it sounded fine?

i have 3 rockford fosgate 1501bd, alpine mrv 1507, kenwood ps401m all with the same problem.

the car is e36 m3 evolution with the battery in the boot. i've used the ground where the battery negative cable is attached.

i am using 2 jbl 1600, single 4 ohm voice coil. both are wired as 2ohm. the amp is mounted on the boot floor in front of the subs.

when i first set the gain up it sounded as it should. then the level of bass went down and sounds distorted.i turned it up a litte bit to see if it makes any differenc. i also turned up the remote bass to get more bass.

For an amplifier, Vibration is the enemy.  Have you brought any of the amps to a repair shop to see what is happening to them?

if it was vibraton wouldn't the soldered joints become lose? there isnt' anything loose inside the amp.

my freind had a look but couldnt work out why it was distorting or as to why it happened.

i have replaced the subs and the checked the tinsels etc.

the battery voltage is around 12.5 and around 13.8 -14.2 volts with the engine started.

on a hard bass not voltage goes down to 11 and then pops back up.

if the rectifier was fried what would the symptons be?

A fried rectifier can exhibit many different problems, including strange amplifier behavior.  You can have your charging system checked and know instantly.  It is also possible your subwoofer enclosure is sized wrong and causing the speaker voice coil to overheat, or the speaker has a partially separated voice coil that is causing distortion after it heats up.  A speaker can appear to be fine sitting cold on the bench but actually be fried.  This is especially possible if the problem exhibits after a time operating and not immediately at turn-on.

if the rectifer was knackered wouldnt it cause other electrical components to fail such as bulbs and other gadgets.

do u think its my charging system? if it is why is it destroying the sound output on the amp.

would i be able to test the aleternator my self with a multimeter.

are there any mesaures i can take so this doesnt happen to my new amps.