is this rumblestrutting?

[horsefeather]

our girls (rougly 9m and 3/4m old) have been together about 5 weeks. The last couple days Lulu, the older one has been making a vibrating noise and and stretching out her body and moving her back legs. shes also chasing the younger one.

theyre not fighting and Lollie moves out of her way. Lulu doesnt do it unless lollie is right there and not all the time. right now theyre happily eating out of the same bowl.

why do they rumble strut. is this a dominence thing? could a heat cycle cause this?

 

[Mo & Stubbins & Vani]

You can refer to this guide:
Dominance Behaviours In Guinea Pigs
Yes, they are rumble-strutting, which is a normal dominance behavior displayed by piggies.
Frequent rumble strutting is a fairly normal piggy behavior, but it truly depends on their personality/character combination. Your girls are reaching their teenage months, which may increase tension.
Older sows, usually 1 1/2 years or older, can also develop hormonal problems/ovarian cysts, which often can be identified in sows being almost constantly in season.
As long as there is no aggressive fighting, they sound perfectly fine.