97 Malibu Noise

I have a strange noise I cannot isolate.

- sounds like a warthog (groan or grunt)
- comes from front center bottom of car
- happens on open highway at all speeds
- does not happen when turning
- seems to be present when driving over slight wave in road
- does not happen when hitting real bumps
- i have checked sway bar bushings and sprayed them
- cannot duplicate by rocking car
- i have sprayed body mounts
- i have sprayed spring seats, spring mounts, strut pivots
- i have put rubber where fender meets body under hood
- i have pulled on everything under car and cannot duplicate
- it's entertaining, as it happens sporadically - freaks my dog - funny sound
- could the abs be malfunctioning?

97 malibu v6 4dr

You have a dandy there Thusted. Wish I could help.