Help: Worried about a few things...

My sweet kitty Benz is a 13 year old black house cat and has been acting a bit strange the last little bit.

I pulled him off of dry food a couple of years ago and onto wet food, and I think he developed an addiction to it. In somewhat chronological order:

- Was overweight so made the switch and helped bring him down a little. And because when he would eat dry food, he started drinking A LOT of water immediately after.
- Was fine for a while until about four or five months ago and I started to notice he would meow and scowl incessantly for food, even after he'd eaten. I also noticed the last few months he doesn't drink a lot of water if not any (I'm sure this is probably because the wet diet has a lot of liquid)
- Noticed a small bulge on his bottom lip and switched the plastic bowl to a ceramic one and ensured he couldn't chew plastic around the house (he's always loved doing this and I think he's allergic to plastic cause the bulge went away very quickly after)
- Started waking me up at all hours of the morning by kneading my head, biting my neck, and drooling a lot. Also started peeing outside the box (which isn't uncommon for him, he's always been a bit of a jerk like that). The last week or two it's been right beside the bed on the floor
- Decided two days ago to switch him back to dry food just to see what would happen. The last two days he's been quieter, hasn't peed beside the bed and is back to drinking a lot of water (which comes with a weird gurgling sound when he does). He seems a bit lethargic though, which is what is worrying me. He seems to have used the litter for 1 pee and a couple of poops and peed elsewhere once.

I'm wondering if it's behavior related or health related, and can't afford to take him to the vet for a million tests and wanted to see if anyone has experienced this with their little guys and gals before doing it.

Environmental factors could include that I am a touring musician and sometimes not home a lot (my roommate cares for him and loves him when I'm gone). There are no other pets (we lost his brother two years ago sadly). He doesn't go outside aside from the patio we have (upper floor apt).

If anyone has any advice or things to read I would appreciate it. Preferably without scaring the crap out of me. Thanks!

First thing I would consider is the litter box itself:  Is it cleaned out regularly?  Cats may reject using a soiled litter box.  Has it been moved recently?  Cats are creatures of habit and it may take some time for them to get used to the new location for the box.

Then, not to scare you but, there is the possibility of urinary tract infection.  The fact he's drinking a lot and peeing in strange places.  UTI is very painful, so some of his behavior could be a attributable to pain.  Male cats are more prone to UTI than female cats. 

Dry food will cause a cat to drink more.  Wet food will have more water in it so a cat will drink less.  If he's just drinking more overall, kidneys might be the cause.  At 13 years of age, he is a senior kitty and kidney issues can develop around this age.

I would recommend a visit to the vet just to rule out UTI or kidney problems, which if left unchecked, could develop into a very serious problem.  Isn't it less scary to arm yourself with knowledge and move forward with effective action than to remain uncertain and unsure about what to do?

It's definitely not a UTI, he's had one before and it isn't really the same.
Kitty box is cleaned regularly, and haven't moved it.

What kind of kidney issues are you referring to and is there a good site to read up on it?

And the noise when he drinks water in his stomach is the weird part. It's like a gurgle.

UTIs can differ depending on where in the urinary tract the infection is. 

Kidney (Renal) disease can be either chronic (long-term) or acute (short-term) and there may be either disease or the process of failure. Here's a website that lists symptoms:

http://pets.webmd.com/cats/guide/cat-kidney-disease

You can search the internet, there are many sites on kidney disease in cats.

I'm not sure what the gurgle sound you're hearing might be.  If he's drinking fast he might be swallowing some air and that could cause a gurgle sound in the stomach, just like in people.  If he's drinking fast, that would indicate he's really thirsty and that's not really normal for a cat.