I'm not sure how else to explain it other than what I previously posted;
To further elaborate, harsh sounds feel like sand or grit peppering my skin from the direction of the sound. Some softer sounds are more like a very mild tingle, always from the direction of the sound. Another interesting thing that I'm not sure is synesthetic is that if I'm startled (for instance, if a car stops suddenly in front of mine in traffic), I physically feel a strong harsh tingle all over my face, arms, hands, chest, etc.
but I can offer a few more examples.
Gunshots (thankfully I'm not around gunfire very often), cars backfiring, very loud sudden noises feel a lot like being pelted with sand or very small hard objects. It's almost like being pricked in a million different places on the surface of my skin, at the same time, from one direction, and lasts for a comparable duration to the original sound itself.
I also get a very mild physical sensation from less dramatic noises, like a Coke can falling into the bin of a drink machine, for example.
Another example; I work in IT, and currently on my left is a running pc that makes a low constant fan noise. I don't notice it for the most part, but while I was typing out my original post and was trying to think of how to explain the sound -> physical sensation experience, I realized that I "feel" that low constant noise on my left side. It's very hard to describe. It's almost like having a very, very mild goosebumps sensation on that arm, shoulder, leg and that side of my neck, face and ribcage. It's not unpleasant and the only reason I really noticed it at all was because I was focusing on explaining the sensations in the first place. I don't feel it at all on my right.
I startle easily and when I get startled, I do get a very intense pin-prick/"pelted with sand or tiny pebbles" feeling from the general direction of whatever startled me. The intensity of the physical feeling is directly proportional to how badly I'm startled.
I actually found Physics Forums by searching synesthesia on Google.
This thread is incredibly long and I'm still reading through some of the later entries, but I didn't mean to not acknowledge any other contributors. You (Rhody) were the first poster that showed a very large interest in coordinating symptoms/characteristics and so that's why you stuck out in my mind.