Audio Systems: car audio fault finding, rockford fosgate subs, amp connector

Question
hi,
   i have just installed a pioneer p7750 head unit with fokal front splits 6inch with tweeter, rockford power series 6.5 inch speakers in the rear doors, orion 4 channel amp, orion mono block amp and two 10 inch rockford fosgate subs. all speakers are running of the 4 channel subs off the mono block. problem. the rear left hand side speaker cuts in and out. i have checked the connection at the 4 channel and it is all fine. the earthing system i did in the boot is a little dodgy i think it might have something to do with it im not sure. i havent checked connections at the actual speaker yet which is what i plan to do next. is there any other suggestions u can give me as to why it is cutting in and out.

Answer
Quick check;
Swap over the two speaker wires from left to right at the amp connector block. Still on same speaker? Problems lays with the amp output. As for the dodgy earth connections, unforgivable, it takes just along to do it right as to bodge it, slapped wrist and don't do it again, o.k.
If it DID swap sides, then it's the speaker or wires to it.
Run a pair of clean wires to the speaker, still the same? Swap out the speaker, that should sort it.