My 2010 yaris is on its 4th transmission!! Help please

[Uzairlexus]

So i bought a slavaged yaris and after driving it for a month i noticed when a downshift in to second gear the transmission makes a grinding noise i took it to toyota and they said it needed a new transmission and i got a 1400$ estimate but toyta replaced as they didnt know it was salvaged and it was under warranty at a 50000 miles and it was 2010 so i was really happy because i got a rentel and they replaced the transmission, they hpw ever did inform me the i should i get a new pressure plate i denied it. About a week after the new transission no more than 300 miles on it the same thing happened again and i took it back to them they once again said that i needed a new transmission and this i got a new flywheel and a pressure plate out of pocket and they replaced the transmission again and the flywheel and the pressure plate. About 2-3 weeks after a new transmission the same problem came back!! I took it backa nd had it exchanged but about a month after the 3 rd transsmission blew up i mean it would go in to any gears. I had it towed to toyota they said we have to call in a specail toyota mechanic to lemon the car but when he came he noticed it was a salavged title and he voided the warranty and i had to take my car to a another auto repair shop i had a 35000 miles lkq transsmission replaced and i got warranty for it but the transsmission still grinds when i down shit into second unless i double clutch the doesnt mind replaceing it but i want to know why is this keep happening btw the shop is best friends so... I can get anything repaired ... I am located in fremont , ca