Scratchy pops coming from the left channel when I turn up the volume why?

Perhaps an aging tube?

Hmmm.  If we make the pretty reasonable assumption that the volume control is a dual gang pot, I'd still guess dirty contacts.  Have you tried (with the power off) turning the volume up and down vigorously a few times?  In the past, I've had components that had pots with silver contacts and now and then you'd have to work the oxidation off.   

I tried again but this time I sprayed the shaft that turns and I don't here the pops anymore:) Its funny but since spraying it the volume knob feels a little stiff. Well
I am happy the popping is gone Thanks.

Plug in another source component to verify it's the preamp.

It's not shaft you spray (will be the same thing as if you spray kitchen sink) you have to spray POT. To get to it you should remove either top or bottom depending where the pot is mounted. Need to direct the straw DIRECTLY onto the pot and rotate it in/out few...several dozen times while spraying.
Than you need to let it dry for few hours before you turn preamp back on.