After he uses the litter box, have you checked to see what his stool is like? It sounds gross, but it would be a good idea to take a closer look at it. The shape and consistency may tell you a lot.
Is the blood fresh red blood or sticky and dark? If it is fresh blood, he may be straining too hard causing little tears. If his stool is also hard, then it makes me think constipation.
A diet of primarily dry food can lead to dehydration which can cause constipation. Cats generally don't drink enough water... they rely on getting it from their food which is one of the reasons why wet food is so much better for them.
A food from Aldi or Sam's Club is probably a very low quality food as well. A lot of people are not aware, but there are huge differences between pet foods, and a good quality food can really improve the health of your pet. Food, naturally, has a big effect on digestion and digestive problems. It also can have a huge effect on skin and coat health and the amount your cat sheds (and in turn the amount of hair your cat ingests.) There is a lot of info on the forum about diet, so I would suggest doing some reading about what you should look for in a good food so you are able to choose the best food that you can afford. I suspect that this issue might be solved just by a change to a better diet.