Garrard 301 motor and rumble

I would definitely replace the belt. You must order the belt from SOTA. Do not use generic replacements.

You might also have your serial number in hand and request a list of upgrades available for your unit. There have been many improvements over the years. For sure you should consider a new magnetic bearing and platter. 

If records have trouble sealing you will need to send your platter back and have a new mat put on. Records that are warped or dished and won't seal sometimes can be made to seal by starting up the table with the two finger nails pushing the lip of the record down at 180 degrees for three revolutions. records that are dished will seal on one side but not the other. 

If the pump makes enough noise that you can hear it from a distance of 10 feet it will need to be replaced with a new unit. The new ones are much quieter. 
 

@mijostyn  No such worries or anything even remotely similar apply to either of my idler turntables. If there is such a thing as a vacuum hold down system that does not fail, sooner or later, color me surprised. 

If a Vacuum Platter Mat is desired for the 301, the AT 665 or 666 will both be able to offer Vacuum Clamping to the LP.

I have the AT 666 and have heard a pristine functioning model prior to making my purchase.

The AT 666 is a Metal Mat and is the one out of Three owned Metal Mats that creates the leanest of the Mats in their presentation. If this sonic is transferred to being perceived on a 301, the tightening of the Bass might be a interesting alternative presentation.  

I also know a individual with the 665 version and they are quite impressed with its Vacuum capability, I'm not sure how they view it as a sonic influence.    

@fsonicsmith 

No, you just have to replace a noisy idler wheel every couple of months or so. 

The actually pump Sota uses is child's play to replace and readily available. If you can come up with a better way to perfectly flatten a record and mate it to a mat of the same mechanical impedance color me surprised. 

It appears you are an antique collector and not interested in the highest levels of performance. I have an old Nagra Tape Machine on display, beautiful thing. I never use it.  

One key to really good LP playback is a robust drive in the turntable. That is why the Garrard has a following, along with the Lenco, Empire and Technics.

No matter how speed stable with no LP, a wimpy drive will have speed variation when you set the needle down and could have more when there is heavy modulation since the drag on the arm is increased.

When there is a slight speed variation, IME you hear it as a slight shimmer in the soundstage. I suspect this is because the variation is so slight that you dont hear it as pitch, rather you hear the tonearm tracking force on the groove walls change as the arm oscillates slightly left to right as the skating force changes with the speed.

If this Garrard were my machine, I’d grease the main platter bearing, make sure the motor has a good lubricant (automatic transmission fluid works well) and finally has a good idler, whose bearing also has a touch of light grease.

You can get idlers rebuilt by Russell Industries on the east coast. They do an excellent job. Most of the rumble you get is from the idler, so the more precision you can get out of it the lower the rumble. Its also worth it to make sure the inside of the platter where the idler bears against it is clean, since any dirt/buildup there can add to rumble too.

If the idler has a sloppy fit on its axle, all bets are off. But IME that’s pretty rare.

@atmasphere 

Speed instability is certainly a problem. Most of it is caused by record warping and eccentric spindle holes. The very same irregularities that cause rumble also cause speed irregularity.  The old idler wheel turntables are less speed stable than any high end belt drive table primarily because of the older motors. You could substitute a modern electronically controlled motor so you can have more accurate rumble. Even if you could create an idler drive that were as quiet as a belt drive it would not last long as components wear. 

The point is, unless you are an antique collector do not buy an old idler wheel drive table. There are many excellent modern turntables, either belt or direct drive that are quieter, more speed stable and better isolated. This is not an opinion. It is a matter of fact.