Actually, yes your tires can make a thump, tump, thump sound. It is often caused by an irregular wear pattern that I have heard referred as cupping or scallopping. I began to notice such a noise from the Generals on my '01 Screw at around 17,000 or 18,000 miles. A close inspection revealed that I could actually see the irregular wear pattern and feel it if I ran my hand over the inside edge or the tires. I took it to a dealer who aligned it and told me I needed to rotate the tires more often. Factory warranty on alignment is only good to 12,000 miles, by the way, so that was out of my pocket. I have tried to rotate them more frequently since then, and I now have 82,000 miles on the same tires, and they still go thump, thump, thump. I think I am recently starting to feel vibration, so I will be looking for a set of tires in the very near future.