The cat is releasing his scent. He's 'marking' you as his. My Gracie used to do that all the time, I had to make her stop because she'd do it for ages.
One of my cats does that when she's on my lap...I don't think she does it conciously. When she really relaxes, she starts kneading. She occasionally does it while sleeping.
My cats always had a clawing pole. They need that b/c of their need to sharpen up their little dagger-like claws and cat scratch fever can be dangerous....
And they purr. Really loudly. Then when you touch them they purr even louder. Its like listening to a motorbike.
I have three...one has a soft, quiet purr (though you can feel the vibration even through a pillow), one has a loud, high-pitched purr...and one has a loud, deep, but irregular purr that sounds a bit like a misfiring powerboat. That one also snores. She snores & purrs at the same time...that sound kind of defies description.
Haha! Grace had a loud purr which would settle down when you didn't touch her, but put a hand on her and she'd start up again. Then she'd settle down and I'd hear the air whistling through her nose. Sometimes if she had a blocked nose her purr sounded like a snort.