Some well-known money managers have been badmouthing the financial markets for what seems like a really long time. Peter Schiff -- just as in the early 2000s -- has been correct but early in predicting another crisis. Marc Faber has been calling for a correction in US stocks since 2013, and has now upped his number from 20% to 40%:

Marc Faber: Stocks are about to fall 40%--at least!

(CNBC) - After years of forecasting gloom and doom for stocks only to watch them surge, Marc Faber is sounding the alarm as loud as ever.

Faber, editor of The Gloom, Boom & Doom Report, believes that stocks in the U.S. and in many places around the globe are in a central bank-fueled bubble. And while he can't put a time on when that perceived bubble will pop, he prognosticates that once it does, the outcome will be horrifying.

"For the last two years, I've been thinking that U.S. stocks are due for a correction," Faber said Wednesday on CNBC's "Trading Nation." "But I always say a bubble is a bubble, and if there's no correction, the market will go up, and one day it will go down, big time."

"The market is in a position where it's not just going to be a 10 percent correction. Maybe it first goes up a bit further, but when it comes, it will be 30 percent or 40 percent minimum!" Faber asserted.

But now some new voices, not typically associated with bearish pronouncements, are being heard. Veteran value investor Mario Gabelli was recently quoted (in an interview that focused mostly on his relationship with Warren Buffet's Berkshire Hathaway) to the effect that US equities are priced for perfection:

Mario Gabelli: There's no margin of safety in stocks

...He warned, however, that "on balance there's no margin of safety. If something goes wrong, you'll have the volatility that you had [Thursday]." The Dow Jones Industrial Average, the S&P 500, and the Nasdaq Composite Index closed lower in a choppy session on the final trading day of April, which did finish positive, but just barely.

And Greenlight Capital's David Einhorn is now pointing out that corporate earnings aren't what they appear, with potentially dire consequences for the stocks that depend on them:

Greenlight Warns of Earnings Risk to Market After GE Charge

(Bloomberg) - David Einhorn's Greenlight Capital warned that earnings degradation poses a risk to stock markets already trading at high levels.

"At year-end, first quarter earnings were supposed to grow about 5 percent, but now, they are expected to decline by a similar amount," the New York-based firm wrote in a letter obtained by Bloomberg. "This level of earnings degradation poses a risk to a market trading at a premium multiple of earnings assisted by record high margins."

Greenlight wrote in the April 20 letter that the full-year outlook for Standard & Poor's 500 Index earnings is even worse, because of lower energy prices and a stronger dollar. The firm also said General Electric Co.'s decision to restructure GE Capital would result in a $16 billion aftertax charge that would drain 5 percent to 7 percent from S&P 500 quarterly earnings.

"We think the market is too high if earnings have, in fact, peaked for the cycle, and we have reduced our net exposure by adding more shorts," the hedge fund wrote. Net exposure is calculated by subtracting the percentage of a fund's short positions, or bets on falling securities, from its longs, or wagers on rising stocks.

Markets normally feature a lot of chatter from brand-name money managers who are mostly just talking their books, so it's a bad idea to read too much into stuff like this. But at a minimum, Gabelli and Einhorn are validating the view that this cycle has entered a later, more dangerous stage. It might not end tomorrow and it might take financial asset prices even higher before it runs out of steam, but limiting factors -- valuations, corporate earnings, foreign exchange rates -- are appearing.