Engine lod after going from synthetic oil to Regular oil no knocking anything just sounds loud

2006 Honda Accord bought new abt 54,000 miles
Always put in synthetic oil went to dearlship they did not put in synthic like I asked so last 2 oild changes it has had regular oil always heard you can never do that
now engine started running loud last few weeks do you think the oil has ruined the engine? Heat panal and exhust were checked fine.
Warranty almost up. Do you think Oil ruined Engine need to take it in.
Is there anything else should have them look for?

Engine usually is pretty quiet.
Also service adviser told me (with synthic alsways checked and told it can run down to 15 a indicated in car) Service adviser told me the same I dont think so I always had reg. Oil and heard to chnage at 3,000 miles
Thank you for your time.