I'm sorry to hear that your fellow Fonzie isn't himself with lots of stomach gurgling, and lack of an appetite after tearing open a plastic bag containing his food and eating a new type of treat last night.
The noises that you are hearing are the result of ingesta moving through the gastrointestinal tract and gas bubbles. In most cases they are completely normal and seem to cause the dog no distress. But in cases where the dog acts uncomfortable it is likely that the pup is experiencing some reflux or abnormal motility, or painful intestinal spasms that are more than the usual. Given that he had more than the usual amount of stool passed this morning I suspect he does have some painful gut spasms.
In severe cases this can be linked to pancreatitis which is a painful inflammation of the pancreas leading to increased enzyme leakage.
Possible causes for his symptoms include a change in diet or treats, dietary sensitivities or allergies, or eating things that he should not have like too many fatty table scraps or garbage, bones etc. Metabolic organ failures (kidney or liver disease), Addison's disease (hypoadrenocorticism), pancreatitis, inflammatory bowel disease or even infiltrative cancers are other possible causes.
Given his history I would think the new treat may be the culprit, or perhaps he did ingest some of the plastic bag.
I can give you some suggestions because he isn't actively vomiting, but ideally if he isn't coming along quickly over the next couple of days I would recommend checking basic blood tests on him including a complete blood count, biochemistry panel and a blood test for pancreatitis called can spec PL (canine specific pancreatic lipase) which is highly specific for pancreatitis.
If his electrolyte levels seem unbalanced (high potassium and low sodium) then testing for Addison's disease with a test called an ACTH response test would be reasonable.
If those things are normal then the next step diagnostically would be an abdominal ultrasound and endoscopy to collect intestinal biopsies. I doubt he will need that level of testing, but I wanted to be complete.
But for now here are some suggestions.
For now to help with gastrointestinal upset and reflux you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one 20mg tablet per 40 to 80 pounds of body weight every 24 hours
These are acid reducers and should help him feel more comfortable. They are quite safe and can be used for a few days if needed. In some cases dogs remain on them long term if this is a repeated problem.
I would pick up all food for now and water for a couple hours to allow his stomach to settle after the acid reducers. In a couple hours you give him water or low salt clear broths like low salt beef or chicken broth to drink, but make sure it is in small amounts only.
If he seems to feel better tomorrow morning offer a bland diet mix of 1/3 boiled, minced, white, skinless chicken or boiled, lean hamburger, all fats drained off the meat after cooking, and 2/3 boiled, plain, white rice, mashed potatoes or pasta mixed with some low salt chicken or beef broth to make it easy to lap up and swallow as well as increase her fluid intake. If he refuses that you can offer a little meat baby food. If he refuses both then he likely needs to be seen by your family veterinarian.
Probiotics such as Fortiflora, Proviable, or Benebac can be added to the bland diet mix to help replace appropriate bacteria.
If things go well and he eats and seems more comfortable feed him the bland diet for 2 to 3 days then slowly start to mix back in his regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert him back to his regular diet.
If he is lethargic, begins to vomit, runs a fever (more than 103F rectally), or has a tense painful belly then he is not a candidate for home therapy and must see a veterinarian for an examination, diagnostics, injectable anti-nausea drugs intravenous fluids and supportive care.
Please let me know if you have any further questions.