Noticed driving home last night that at one point in 4th gear under 3,000 rpms going 45 or something the car started vibrating ALOT...when i let off it would stop ge tback on it and it would do it again...then when i came to a stop light and drove back off it didnt do it again and wasnt doing it at all...but today it happened again....engin mounts or what is this?

 

i noticed that as well but mine was on rt95 going about 70-80 o thought maybe the roads ....because i havent noticed it much more