While towing my 26" toy hauler, If I hold down the brake hard the front left brake makes a POP sound. What could be happening? It feels like it still works good.

Could be a bushing issue in the a arms, or a ball joint issue, need a frontend shop to check it out.

Or just put a jack under the a arm, and get the tire just off the ground, and use a crow bar and put it under the tire and slightly lift up on it, if there is any major movement, you have a suspension issue, ball joint, wheel bearing ect....

Get it checked out.

Also wait for others to chime in, they will have other ideas, so wait before you spend the money at a front end shop.

It's new, So I hope I will not be forkin out any money;)