I am a owner of 02TL-S and has the stock 6 in-dash bose head unit with an after market 12inch sub. For some reason after I dropped off my girlfriend and started my car up, my after market base started to bump like crazy with no sound coming out of the speakers. Even though I turned off the head unit the bass buzzing like crazy so I decided to disconnect the sub, after doing so I noticed that I hear some music but only really low coming out of the stock sub! Can some one tell me what is going on? I went to a local audio shop they say that the head unit is messed up and they said that I need to change the head unit,is this true?

Another question I have is, if I do have to change my head unit what is a good head unit? I want to get one with a monitor! The audio shop recomended to buy the kenwood KVT-617DVD for 900 dollars but I also found a PIONEER AVH-P5700DVD IN DASH FLIP UP MONITOR for 700 dollars but it is used.

Any suggestions? Any idea what happened to my head unit?
Thanks in advance