Why is my dog's stomach gurgling, not eating, and butt scooting?

Garling noises are called borborygmi and this can be normal stomach noises, but when heard along with lack of appetite this suggests gastritis (inflamed stomach). Gastritis can be cause by many things including dietary indiscretion (eating something he shouldn't have), FB ingestion, and many organ malfunctions. The rubbing of the side of his butt on things is also a sign that his anal glands (two sacs located on the inside of his rectum at the 4 o'clock and 10 o'clock position) are possibly full and irritating him. Anal glands are suspected to be caused by allergies and also often get full when pets go through bouts of diarrhea, because normally they are expressed when hard feces push past them.

Because of the multiple factors that are affecting your pet, and the possible need for him to get his anal glands manually expressed to reduce discomfort, I am recommending taking him into your vet for a good exam. If he is found to have some GI upset then an appropriate antibiotics can be prescribed to help him. I would also recommend a probiotic, such as Culturelle over the counter or one from your vet, and a bland diet of boiled plain chicken and rice or cottage cheese to help settle the stomach over the next 4-7 days, then slowly transition him back to his normal diet if all goes well.