Sorry if this is long winded and also hope I have put it in the right section.

I cleaned inside my pc and installed a second dvd rw drive. After starting the pc again there was a continuous droning noise. I tried the dvd rw to check if it worked ok and I can play video on dvd, audio dvds & cds and can load programmes ok with my first dvd rw. Haven't tried recording anything yet.
Took the pc apart again and checked that nothing had been unseated and checked the drive installation again. Checked all connections at the back of the monitor. Everything ok.
Took the new drive out and restarted the pc, still a droning noise.

My sound card is a Nvidia 7300 LE, about 2 years old. Could it be my sound card is on the way out, or gone?
The only way I can mute the sound on the pc is to use the control panel for my monitor, by muting it. The noise is coming from the speakers and not from the tower.

Thanks for reading and in advance for any help offered.
hedley