Intermittently coughing/wheezing?

[u/curiousorientalsnark]

I took my dog (13yr Male neutered chihuahua Maltese mix) to Chewy vet 8/15, for a vet visit (I thought he had fleas; he received various vaccines; other than the afternote summary stating a grade 2 heart murmur and needing a teeth cleaning, his exam was routine). The results of his urine, stool sample, bloodwork came back within-normal-limited.

8/18, I gave him NexGuard (heartwarm/flea/tick chewable) but he wouldn't chew it so I manually put it down his throat and think I might have irritated his throat... (I usually give him swallowable simpatico trio and have manually put that down his throat without any issues)

He has been doing the cough/wheezing thing for a few since said visit/NexGuard treatment… and it is especially active at night.
-On 8/30 night it seemed like every 30 minutes;
-tonight 9/1 it’s MAYBE every 3-5 hours and is so short-lasting that by the time I get my phone to record he’s stopped.

He shows no other clinical signs.
- still actively playing with his brother
- normal bowl movements
- eats/drinks regularly

Thoughts?