2006 Scion tC, Manual Transmission, 148xxx Miles. 

My Scion is in the best condition you could ever find one of these cars in.  
jus recently drove 1,100 miles to Florida and towards the end of the trip, the car would make a short grind/thump noise when I would put the car in 3rd gear when going about 20-25mph ….  Otherwise if I’m at a complete stop and I put it in 3rd, it still makes the same noise.  

Clutch was done 8k miles ago and not sure what they used to for manual trans fluid ….  What could be my problem, please help !!!!

What is something I could do to fix this problem ….  Im somewhat mechanically inclined but ur not gonna find me looking for a needle in a haystack inside a transmission ….  Lol