Adding a Turntable Mat

Also Herbie's has matts of various thicknesses which allows you to dial in your VTA. It can be a challenge to measure the difference from where it is now to where you need to be, but gives you another option.  Especially after added the OL Cartridge Enhancer.

My Experiences  undertaken with changing TT Mats to learn how the interface is affected between Platter and Stylus, has led me to the use of Mats made up of many different materials.
As I have quite a few different materials I have loaned these out to other TT owners for demonstrations of them and comparisons between them in their own systems.
I have heard these Mats on Belt Drive, Idler Drive and DD TT's.
In my assessment there is not one Mat I have used that excels as the most noticeable type across all three Motor Drives.

A Mat that has impressed and has been adopted by other users after my introduction and maintained as their Mat of choice, is a Mat produced from a Material called Forex Foam, this is inexpensive and a good place to begin.
Two Tenuto Mat users are now using Forex Foam as their preferred choice.       

Turntables of this era came with a ribbed rubber mat that does not support the record over the entire playing area. Ken Kessler of Hi-Fi News has been experimenting with mats and weights that fit over the spindle, in recent issues. These are all relatively inexpensive, so much so that one can try and sell on if need be. I had a Pioneer PL-12D and started by inverting the rubber mat placing it ribbed side down. Cork or felt mats are worth a try. I replaced the headshell on mine, which was better than the standard issue. A new drive belt might also be appropriate.

Don't worry about the VTA. It changes anyway with different cartridges.
You want to remove the rubber mat and adhere the cork mat to the plater with a spray contact cement. The mat should have a depression for the record label. Lacquer thinner can always remove the contact cement. 

Lots of good advice here!

I second the motion to lubricate or make sure the bearing on your TT is properly lubricated! A good habit to get into is to check that on an annual basis or more frequently, depending upon how much you spin your records.

With regard to TT mats, if you haven't done so already, I would recommend some reading on Analog Planet and/or Stereophile, among other reputable publications. If memory serves correctly, I believe Michael Fremer may have done an article or two on this and I don't think he's fond of felt mats. As I recall, I think he said they generate static electricity and would wreak havoc on a stylus in an oops moment.

Before experimenting with mats, I would recommend using a record clamp if you aren't already. I very much like and have been using this one for quite some time now:

Michell - Reflex Record Clamp | Shop Music Direct

Check the spindle clearance on your Pioneer to make sure this will work or just ask Michell, Music Direct or whomever.  There are other less expensive clamps like The Record Doctor and a few others. I've never used anything other than the Michell and found I don't need to use the included optional washer recommended for significantly warped records. I only have 1 record with a slight but significant warp. It's unplayable without the Michell clamp but plays beautifully with it and no washer. Record pucks or weights accomplish the same idea. However, I've never liked the notion of putting significant extra weight on a TT bearing.

If you decide to do the record clamp or weight thing, just for fun, play your favorite record without the clamp or weight, first. Then, play it again with the clamp or weight right afterwards. I wasn't expecting much when I did this. However, I was quite pleasantly surprised with the results.

Good Luck!  And please let us know how you make out!