Hi,

1. a couple of possibilities come to mind. The most obvious to me, is brake pads worn to wear indicators, and the indicators are doing their job - giving you an audible warning as they scrape against the spinning rotor. They may have been close before, but towing the trailer wore the pads down quickly to a point where the wear indicator (metal tab on the pads) started scraping the rotor.

A second possibility is a bad wheel bearing, although it usually makes more of a rumbling sound. Heavy trailer hooked up to the car may have put enough extra load on a worn wheel bearing to make it quickly get worse. A bearing that has play could allow the brake rotor to ride crooked, letting it rub against a metal splash shield. I would expect the noise to go away or diminish when brakes are applied, because the force of the brake pads squeezing the rotor would try to straighten it out. This is much less likely but a possibility nonetheless. Is there any roaring or rumbling sound present?

2. I would check the brakes before your long trip. The wear indicator usually starts making noise when there is still some brake lining left on the brake pads.

If you take it to a shop and they can't find anything wrong with the pads, have them look for bearing play.

3. As I said, towing a trailer puts more load on the brakes and may have been "the last straw" for already worn brake pads. It would explain it very nicely.

If you take it to a shop, they can run the car on a lift with the tires off the air, in gear, and listen to each wheel bearing or other parts near them, with a mechanics stethoscope.

The brake pad lining on new pads is roughly 3/4" if not more. The wear indicators make contact somewhere around 2/32 or so, they are extremely crude.

Depending on your wheel design, you may be able to see the outer pad through an opening on the wheel.

Jan