I suddenly heard alot of distortion when playing the Pioneer PL-990 turntable. Wonder if replacing the needle may take care of the problem.

Depends on the circumstances. Is it only when you play it loud? Air- or room-borne vibrations will feed back through the TT to the speakers. Keep the volume down to avoid it.

If you call the stylus a 'needle', replacing it maybe beyond your capabilities. There are lots of reasons for TT sound to be less than perfect and arbitrarily replacing things can do more harm or introduce new problems. Take it to someone experienced and equipped to evaluate the issue.

Tonearm balance, antiskating, dirty stylus, feedback.

I just got ripped off by buy this same turntable and it has the same distortion problem.