The big boys
I have heard the bloop of outgoing mortars (in Tiktrit), but anything incoming is usually way too far away to hear. My limited experience with mortars is that they fall fast and explode with a loud pop or bang, rather than a drawn out explosion like on TV. 60mm mortars are pretty short ranged (about half a click), with the distance increasing with the caliber (82mm, 120mm, 160mm).
Rocket-propelled grenades are different than rockets, despite the name. The most common RPG is the Russian RPG-7, which is 85mm in diameter (larger than a hand grenade). They are really little more than large grenades flying slowly through the air, and leave a smoky tail behind them (really neat to see at night). They make a whoosh or shoushing sound, and can land somewhere near where they were aimed at ranges up to about 500m.
Rockets are the scary ones. They sound like a metallic, clangely, freight train coming in, if you can imagine that. They don’t sound anything like what you’d imagine a streamlined object on a pre-determined ballistic path would sound like; more like a kitchen sink with all of the plumbing just tum-tum-tumbling through the air. Rockets come in sizes from 107mm to something over 300mm, and have pretty long ranges (just over 8,000 meters to something near 300 kilometers!). We’ve been hit by rockets a couple of times, but I was only close enough to hear them once.
The Muj does not have artillery, so far as I know. Although there was a battery of US Field artillery dug in at Tikrit, I never saw (or heard) them fire. I have also never heard a tank fire.