Justin Bieber Yodels at Coachella after Hearing Mason Ramsey

Justin Bieber got yodeling fever at Coachella Friday ... proving that Walmart kid has truly taken the country by storm.

Justin hit up Mason Ramsey's performance at the music festival ... where he serenaded the crowd after being invited up on stage by Whethan.

The crowd went crazy for Mason as he yodeled "Lovesick Blues" and Justin was impressed enough to carry the tune as he walked from the concert.

We're told Manson and his people -- yes, he has people -- are in touch with Post Malone and his peeps, for a triumphant return to Coachella weekend 2.