Currently shooting 2015 hoy Nitrum bu am noticing it seems to be getting loud. Thinking about trying out a Mathews, as they seem pretty darn quiet, dead in the hand, and smooth. What's your opinions on the quietest bow in the last 2-3 years-current?

Surprised they actually don't advertise as the most quiet.... It would be a great selling point I would think.

One shooting a heavy arrow.

While I'm not a Mathews fan, you'll be hard pressed to find a bow quieter than the Lift or Phase 4

Well I shoot the Phase 4 and it's very quiet. I wish I would have waited to try the Lift but am real happy with the Phase 4.

IMHO - in order of my experience

Mathews HTR - scary quiet with a 450 grain arrow, smooth, but slower FPS.

Mathews V3X - very quiet with the same arrow, still smooth, a little faster.

Mathews Phase 4 - same as above, maybe a slight bit quieter. Very smooth, fast, and dead in the hand over the first two.

The heavy arrow helps all of the above with less volume of sound.

YMMV

If it was quiet before and is getting louder.........check your specs.
Suspect string/cable stretch and more cam slap.

PSE is my preference. Quiet enough for spooky deer here in Ohio.

I would question if your bow is just out of tune. I am a believer in Carbon riser bows from the Carbon Riser of the Carbon Spider offerings to the CD34 & up to the RX offerings since.

For me the CD34 has been the quietest bow I have had the good fortune to put to use. way more bows out there that I have not handled for one reason or another.

Tuned recurve with a heavier arrow and beaver string silencers.
Whisper quiet!

A heavier arrow will most definitely help! I currently use a couple year old Elite Enkore, very smooth and very quiet. Out of all the bows I've used over the years, I like the Elites better.