Well Recently My PSP 1004's speakers have been getting rather Crackly especially with Higher pitched noises, especially for instance the default game start noise.
Then looking around for any tips on how to fix this problem before actually looking into replacement speakers at Dealextreme, I found this:
Surprisingly... it actually worked and fixed my speakers, my left one made a tiny pop sound and its been perfect again since!Pucker your lips over the speaker hole... then suck real hard... you will hear a crackle or pop... now try it... it may take some time but it normally works... I too thought my speaker was blown and saw this little trick somewhere and it worked a treat... have to do it once in a blue moon... also if you don't have the auto volume limiter on you will pop your speakers more often.