In order to clear a sink drain clog in an upstairs bathroom this weekend, I
needed to remove the shutoff valves to get clearance to remove the P trap.
This entailed turning off valves in the basement for the lines that supplied
the upstairs bathroom. Everything went back together again and, after some
initial spluttering to rid the air in the lines when I first turned the
water back on again, all seemed well. However, sometimes if I open the
faucets only part way, a hammering starts in the pipes and the water turns
off/on about 4 times per second. If I open the faucets further, the
hammering stops. This happens in the sink faucets and the shower, which are
fed by the same supply lines and happens in both the hot and cold sides.
This never happened before I shut off the water.

Is there anything that I can do to get rid of this problem without having to
install water hammer arrestors? Since this never happened before, I don't
want to tear into my walls if I don't have to.