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

Stop it

A blond in the Mercedes Benz got struck by another blond in pick-up truck and got her rear bumper corner bent.
The one in pick up truck advised one in Mercedes Benz to blow the exhaust pipe to pop the bumper out.
She started blowing the exhaust pipe and was blowing for an hour with no success.
Another blond passes by on foot and asking why she blows the exhaust pipe on her Benz... Than she noted that she didn't close sunroof...

Jiggle the power supply. Make sure it is plugged in to the input on the back.  Secure it.

Sounds like the name of a new breakfast cereal.

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.

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

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.

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.   

Perhaps an aging tube?