My neighbor's pool pump did the same thing to me last summer. I was set up on my patio shooting the Veil Nebula and could not figure out why half my subs had this weird oval star shape. Drove me nuts for two weeks before I noticed the pump kicked on at 9pm every night like clockwork. Moved my rig to the other side of the yard behind a shed and the problem vanished. Now I check what is running in the house before I even set up. Water heaters, AC units, even the fridge compressor can send just enough shake through the floor to ruin a good sub.

Short subs really do dodge a lot of the wind and sky glow problems that long tracking runs run into. Tracking still wins for the faint stuff though, try pulling the North America Nebula at 8 seconds and you just won't get the same signal.

Read a thread on r/bikecommuting about this and a lot of people said the shower thing sounds good until you factor in the wait. One guy said his office only has two stalls for like 200 people so he gave up and just brings a small towel and baby wipes. He said he changes his shirt and socks, wipes down, and nobody has ever said anything to him in three years. I mean 7 miles is a real ride though, so maybe it depends on how hard you push. For me the wet hair thing would bug me more than carrying the bag.