Sirspeedy, your description of the problem sounds like a static discharge to me. If the arm is improperly grounded it is possible for it to *not* hum, but have discharge problems, especially with low humidity. The needle tracking the LP will create the static charge and if not drained off by the grounded arm, you will get a random static 'pop', which can be quite loud once amplified by your electronics!
A hint is that this problem showed up when you changed arms. If the prior arm is available, I would swap it in and see if that sorts it out. If not, I would test the arm to see if it is really grounded correctly. BTW the turntable should be grounded to the arm too. If not, that can cause static discharge too.
A hint is that this problem showed up when you changed arms. If the prior arm is available, I would swap it in and see if that sorts it out. If not, I would test the arm to see if it is really grounded correctly. BTW the turntable should be grounded to the arm too. If not, that can cause static discharge too.