Unusual probelm with my turntable

You should write what kind of TT and arm and cartridge.
What comes to mind is a damaged wire in the arm, where it exits the base of the arm under the platform. A bare spot touching the metal directly there when the arm is lowered?
OR (worse) inside the arm where it comes out to enter the arm base.
Perhaps it was damaged before, but did not make direct contact, and moving the table around etc, has move the wire just enough to cause it to touch.
This is only a guess, but a reasonable one.
Question to answer: is it in only one channel? My guess is more likely if the buzz is in one channel.
You can take the base off/open the base and see if the wires are touching the tube, and if they are damaged.
I personally would push them up into the base of the arm bbase a bit, and make sure they 'float' in the middle of the armtube's base exit.

Thanks for your response Elizabeth. My system is just entry-level, the turntable is a Pioneer PL-A45D attached to a Musical Fidelity phono stage, Dared integrated amp and Monitor Audio speakers. I can hear the buzz from both channels.
The shop that installed the cartridge tested the unit when I came to pick it up and it was quiet. I was worried on the drive home because the roads were a little bumpy and I could see the table bounce up and down and I thought that something might get loose. I will take your suggestion and look at the wires of the tonearm.

And you posted this in the speaker forum, why?

Shakey

I was worried on the drive home because the roads were a little bumpy and I could see the table bounce up and down and I thought that something might get loose. I will take your suggestion and look at the wires of the tonearm.
Rangefinder (Threads | Answers | This Thread)

When transporting a turntable, the platter needs to be removed so the bearings don't get damaged. I'm sure this wouldn't have caused the problem your having though. I mentioned it so anyone reading this doesn't transport one around and damage theirs. It would cause a low frequency rumble sound through the speakers if they get damaged.