ticking pvc pipe from gas furnace

i have a 90 plus gas furnace the problem is the vent pipe that runs through the crawl space keeps ticking when the furnace is on and then for a short time after the furnace shuts off is the vent pipe which is sch.40 to long.is there any set distance for this.it runs under a crawl space about 30ft to the outside
thanks
george

There is a table in the furnace installation manual that will tell you the maximum length allowed for your vent. It is based on the pipe size 2.5, 3, 4 etc. plus the number of elbows in the vent piping not including the termination elbow. I would check there first. Also, does the pipe slope upwards away from the furnace? Or is it sloped down or have a valley (a low spot in a horizontal section that may hold condensate) in its run?

Most likely heat expansion of the pvc where it runs through support straps, joist's etc. Try covering the pipe, where it makes contact, with a flexible material,

pvc vent pipe

what type of flexible wrap would you reccond
thanks
george

PVC expands and contracts as it is heated and cooled. Any place that it rubs can cause noise. The actual expansion/contaction isn't noisey in itself, it is the friction as it rubs on things. So, anything you can do to make it slide against those spots where it is rubbing will help. Maybe even a sheet of wax paper. They do make rubber covered hangers for the pipe, too.