Mastodon frontman Brent Hinds recently posted on his Instagram a photo of Dave Grohl, with the meme caption, “Making rock n roll safer with every red carpet all star jam.” (Hinds has since deleted the image from his own feed, but that’s it above.) Coming from Hinds, the jab feels slightly pot-kettle-black-ish, as Mastodon are among the safer bands in “extreme metal” today, largely due to the fact that they’ve sanded down their prog/epic tendencies on recent releases in favor of an accessible sound that bears a distinct resemblance to that of former tourmates Queens Of The Stone Age (for whom Grohl plays drums on occasion). Even so, Hinds’ snark is not without substance: Grohl might be the nicest guy in music, and he’s obviously one of the best drummers of his generation, but the choices he’s made over the last decade-plus suggest he’s more interested in using his reputation to cross items off his bucket list and bridge the gap between the Boomers and Generation X than he is in making exciting, innovative music. I mean, guy played on Nevermind, In Utero, and Songs For The Deaf, so he has a lifetime pass, but the newest of those albums is now 12 years old.

Anyway, there are two brand-new pieces of evidence further supporting Hinds’ diss:

1. HBO has announced that Grohl will produce his own series for the network, and it will serve as an extension of his Sound City documentary, in which he told the story of the legendary now-shuttered studio where Nevermind (among countless other albums) was recorded. In the new series, Grohl will reportedly visit studios across the country, and interview the artists and engineers who have worked there, including Steve Albini, Ian MacKaye, Paul Stanley, and Nancy Wilson.

2. The next Foo Fighters LP will reportedly include a collaboration with Eagles guitarist Joe Walsh. As Walsh told Billboard, “I joined the Foo Fighters for two days and I played on a track of theirs that’s gonna come out … my drummer when I play solo, Drew Hester, is a great friend of all of those guys, so I hooked up through him.”

Is collaborating with Joe Walsh in 2014 “safer” than collaborating with John Fogerty and Rick Springfield in 2013, or with Paul McCartney in 2012? Eh, it’s probably like six of one, half dozen of the other, square root of 36 of the other-other (or 6-6-6, ironically). But Grohl has done all that stuff and more. Of course, he’s also done collaborations with weirdos like Ghost B.C. and Teenage Time Killer, which isn’t safe so much as … random? In any case, it seems safe (har har) to say he won’t be working with Mastodon in the near future (which is totally OK, as that band’s drummer, Brann Dailor, might be one of the few guys in the game on whom Grohl wouldn’t be a clear improvement). UNLESS — maybe? — Grohl’s new HBO series does a segment on Rock Falcon Studios, where Mastodon recorded their upcoming LP, Once More Round The Sun, with producer Nick Raskulinecz … aka the guy who produced the Foo Fighters albums One By One and In Your Honor.