if the hooting or sneezing is temporary and connected with a new bag of hay or eating on the day etc., then it is just a slightly blocked nose that will clear with either a sneeze or eventually after a day or so. Guinea pig airways are very narrow, so you hear every little obstruction in them very clearly. The VAST majority of cases of hooting falls in this category.
If the sneezing gets worse, the hooting turns into loud and persistent crackling and your piggy is starting to lose its appetite, then please see a vet for URI (respiratory tract infection) promptly.
Before you start thinking about heart problems, you need to have regular hooting for weeks, not just a day or two, and you want to see it in combination with other potential indicators of heart disease.
@helen105281 can give you the full list if you wish to, but in your case I would really not worry! Since hooting has hit the online world as a potential heart disease symptom, we get regularly posts from worried owners.
It is not easy to diagnose heart problems in the first place; a guinea pig can show several symptoms on the list and STILL not have a heart problem (I have been there with piggies of mine). The ones that turned out to have a problem (irregular heartbeat), didn't show any symptoms and didn't react to heart meds. They have been seen by a very experienced guinea pig vet.