Please Help with thump sound

ok so here is my problem. my truck gets driven in moderate amount of mud but not like off roading. this is done to get to my work. on nights when its 20 degrees or colder i get a lot of suspention thumping sounds. if the roads are dry it will continue to make the thumping sound all the way home(which is 80 miles on highway). but if there is any standing water thats not frozen i can drive through it and the thumping stops. could my bushing be getting hard from the cold and if so can i spray something on them. it only happens in the winter

 

am i the only one haveing this problem. i have looked at searches over and over and no one seems to be haveing this problem. any info or sugestions would be helpful

 

Is the noise coming from the front or rear? Are you running stock suspension?

 

Check your mud flaps.....

I had a similar thumping and my flaps were broken where they come in contact with the body.

 

the sound is in the front and im all stock no mud flaps