Even if a "quiet pad" to mount the drive internally was available, there's just not a lot of space inside the MBPro, which would seriously limit what you can do with that kind of solution, even if you could ignore heat (please don't ignore the heat!)
You COULD remove the hard drive, put it in an external case. The drive will still be noisy, and you might come up with a padded box of some kind to keep the drive in/external fan forcing air to keep the box and drive cool. Makes it a little less portable, I think, but it's a possible solution....
Change out to another drive, maybe another brand. Some drives, even the same brand and model, can be quieter (or noisier). You may get lucky and find one that fits your need for (less) noise...
In my somewhat-limited experience - simply replacing the hard drive with a new model (regardless of brand and model) may give you noticeably less noise. Like I say, sometimes you can be lucky.
😀
And, finally, if you do get tired of the incessant noise of a spinner, you know what you can use to replace it with silence.
SSDs do continue to go down in price. You can find decent Crucials, 512 GB, for under $200 now.
I did find an article testing a variety of mostly current hard drives
http://www.silentpcreview.com/article29-page2.html
That listing points to W-D Scorpio Blue at the top of the noise list (quietest, at least in that report)