Odd noises!

Sent my car for the regular 20,000km maintenance last month, which they did a tire rotation, i.e. switching front & back .
Afterwhich, for the past month, while driving, I began to notice a "whopping" sound that seems to be going along with the wheel's rotation & seems to be getting louder.
My 1st suspect was that there may be some issues with the tires, however, there doesn't seem to be any abnormal vibration nor drift as far as the steering wheel's concerned, while the usual tire rolling resistance noise is still there.
Just to be safe, I've decided to bring my car to the Toyota dealer for them to do a further analysis.
While awaiting for their "test" results, appreciate it if anyone can give me some idea of what might be happening.

Thanks!

 

Well, based on the dealer's report, it turns out that the Dunlop tires are the culprit! Anyway, they'll be writing a report to Toyota Thailand & I'll have to wait a week for the outcome.