I have a EX-351d that I've had since 2003 and it's played like a dream, even with the stock EMG-HZ pickups. A few weeks ago I got back home from college and played it, but it sounded really muddy..kind of like how a really low end guitar sounds. Is this a pickup problem? Should I just get new pickups or go and have everything checked out?
Perhaps it is in need of a string change. If your room doesn't have a dehumidifier or is very dusty, the strings could be rusty, dirty, or both. I would perform the string change first, throw some lemon oil on the fretboard (given that it is not maple) and give your axe a good polish. If that does not solve the problem, big deal; you spent 6$ and an hour of your time taking care of your guitar. Also, check the output jack on your guitar for insects. Seriously, I had a spider crawl into my loadspeaker output jack on my Marshall amp head and it died in there. Amp sounded like shit until I fished it out with needlenose pliers!
Also, check your cables. Sometimes they just lose their integrity; I just threw out an old (cheap brand) cable 3 days ago that measured on the order of kilo-ohms resistance. Sure, it still worked, but barely. If you have multiple guitars, test your amp and make sure that it sounds alright also. Just treat this as conservatively as possible before taking invasive action (replacing hardware, disassembly, etc) on your guitar!
Thanks for the help, I changed the strings and applied some lemon oil, checked the jack but it still sounds like crap =( I also have a grassroots forest which used to give off slightly less output than the EX but now it's tone rips the EX apart.